For now, "there will be no modifications" to current policy, Gen. Joseph Dunford, chairman of the Joint Chiefs of Staff, said in an internal memo to all military service chiefs, commanders and enlisted leaders. That was despite Trump's announcement Wednesday on Twitter that he will not "accept or allow" transgender people to serve in the U.S. military.

By late Thursday, the Pentagon still had nothing more to go on than the tweets, a highly irregular circumstance that put Mattis and others in the chain of command in a position of awkward unease, if not paralysis. A commander in chief normally works out policy changes of this magnitude in advance in order to preserve order and morale.

Trump's tweets drew quick, sometimes scathing criticism from many lawmakers, both Democratic and Republican, as well as many military troops and retirees. But social conservatives applauded. Protesters demonstrated in several cities as well as outside the White House.

Dunford began his memo to the nation's military leaders: "I know there are questions about yesterday's announcement." He said nothing would change until the president's direction had been received and developed by Mattis into written "implementation guidance."

"In the meantime, we will continue to treat all of our personnel with respect," Dunford wrote. "As importantly, given the current fight and the challenges we face, we will all remain focused on accomplishing our assigned missions." That last statement appeared to reflect a concern that confusion over Trump's tweets might distract troops, who are engaged in dangerous operations around the world, including shooting wars in Afghanistan, Iraq and Syria.

White House press secretary Sarah Huckabee Sanders said guidance on how to "fully implement this policy" is still to be worked out. Asked whether Trump realized he could not change the transgender service policy via Twitter, Sanders said, "I think he was making the announcement of the policy change," even though no specifics had been worked out.

Mattis has been on vacation this week and has been publicly silent. Sanders has said Trump informed Mattis of his decision after he made it on Tuesday. It was Trump's judgment, she said, that transgender individuals are an unacceptable cost and distraction for the military and should not be allowed.

Dunford was not aware that Trump was going to announce the ban, a U.S. official said. The official was not authorized to discuss the matter and so spoke on condition of anonymity.

The top Air Force officer, Gen. David Goldfein, sent a note internally to his entire force Thursday citing Dunford's memo and saying that he and Air Force Secretary Heather Wilson "emphasize that all airmen will be treated with dignity and respect as we work through the potential policy changes" coming from the White House.

Together, the Dunford and Goldfein notes illustrate that military leaders did not equate Trump's tweets with legal orders.

Gen. Mark Milley, the Army chief of staff, made similar points during a speech at the National Press Club.

"I have yet to receive implementation guidance" from Mattis, Milley said. "We'll act when we receive directives through the proper chain-of-command channels." Until then, nothing changes, he added, citing the Dunford memo.

Trump's announcement caught the Pentagon flat-footed in a way rarely seen in the recent history of civil-military relations. The Pentagon has not released data on the number of transgender people currently serving, but a Rand Corp. study has estimated between 1,320 and 6,630, out of 1.3 million active-duty troops.

"Please be advised that the United States Government will not accept or allow Transgender individuals to serve in any capacity in the U.S. Military," Trump tweeted, even as hundreds, if not thousands were already serving. The implication of the pronouncement was that those now in uniform would be forced to leave.

Trump wrote that he had consulted with "my generals and military experts," but the White House has not identified them and none have come forward. Just last week, when asked about the transgender issue at a Senate hearing, Gen. Paul Selva, vice chairman of the Joint Chiefs of Staff, said, "I am an advocate of every qualified person who can meet the physical standards to serve in our uniformed services to be able to do so."

Transgender service members have been able to serve openly since 2016 — a policy applied only to those already in uniform. The Obama administration began a review of the costs and benefits of allowing transgender individuals to enlist, and less than a month ago Mattis extended that review for another six months. Mattis said then that this "does not presuppose the outcome of the review," but Trump's tweets appeared to have done just that. There had been no presumption that the extra six months was a prelude to a total ban.

The American Civil Liberties Union said its chances of getting a court to block Trump's proposed ban might depend on the details of the plan.